1. Field of the Invention
The present invention relates to a surface-mount antenna device that allows communication in two frequency bands and a communication apparatus such as a mobile telephone that uses the same.
2. Description of the Related Art
FIG. 9 shows a conventional antenna device that is adapted to communication in two frequency bands. In FIG. 9 an antenna device 100 comprises two patch antennas 101 and 102 that have different resonant frequencies and are disposed side-by-side with a certain spacing to allow both of them to be connected to a single signal source 103 via capacitance coupling. It is thus possible to construct an antenna device that responds to two frequency bands by disposing two patch antennas with different resonant frequencies side-by-side.
However, in such type of antenna devices, too small a space between two patch antennas 101 and 102 tends to develop undesirable interference between the two patch antennas, preventing obtaining desired characteristics. It is necessary to widen the space between both of them to 3/10-wavelength or more to reduce the mutual interference between the two patch antennas to a negligible amount. This presents a problem of enlarging the size of the antenna device as a whole.
Recently, downsizing of communication apparatus such as a mobile telephone using the antenna device has been promoted and the configuration of two patch antennas disposed side-by-side will present difficulty for further promotion of downsizing of the communication apparatus. Thus, the present inventors have been engaged in developing the technology for manufacturing an antenna device in integrated circuit configuration to achieve further downsizing of the communication apparatus. In the first step of developing a surface-mount antenna device having two frequency bands, the present inventor produced a first surface-mount antenna device operating at a first frequency and a second surface-mount antenna device operating at a second frequency and tried to dispose two surface-mount antenna devices in proximity on a mounting board.
However, providing two surface-mount antenna devices reduces productivity in manufacturing the antenna device and presents a limit in achieving substantial downsizing of the communication apparatus. Also, a new problem arose in that gain is decreased if the antenna is downsized to make it of the surface-mount type. The new problem can be reduced by making the space between the antennas smaller but the smaller space between the antennas causes a problem of interference between them.